Electron discharge device



May 7, 1929. H. P. Do'NLE ELECTRON DISCHARGE 'DEVICE med Dec.' 1, 1922IN V EN TOR ATTORNEY Patented May 7, 1929.

UNITED- STATES 1,712,032 PATENT OFFICE.

HAROLD POTTER DONLE, OF MERIDEN, CONNECTICUT, ASSIGNOR, -BY MESNEASSIGN- MENTS, TO RADIO CORPORATION OF AMERICA, A CORPORATION OFDELAWARE.

ELECTRON DISCHARGE DEVICE.

. Application :tiled December 1, 1922. Serial No. 604,312.

M v invention relates to electrical signal receiving apparatus, and moreparticularly to instruments utilized in the reception of intclligcnce byradio telegraphy or telephony.

The primary object of my invention is to provide a detecting` andintensifying system of great delicacy in point of responsiveness to weaksignal impulses but of sutlicient stability and uniformity of operationto permit even untrained users to secure good results. Further objectsare to select or discriminate between radio or other high frequencysignals having different frequency characteristics, to produce notmerely a loud but a faithful and undistorted response to receivedsignal-energy, and to control the action of the entire receivingassembly witha minimum number of adjustments.

I have discovered that by modifying the construction of a vacuum tubeand by utilizing this modified tube with circuit arrangements andadjustments differing from those of the prior art, a substantial andexccedingly useful increase in responsiveness may be secured.

Fig. 1 is a longitudinal section and side elevation of one form' ofvacuum tube which I have found satisfactory.

Fig. 2 is another sectional view taken on a -plane at right angles tothat of Figure l.

Fig. 3 is an end view of the lower end of such a tube.

Fig. 4 is a diagram showing a circuit in which the tube may beeffectively used.

My new-vacuum tube in its preferred form differs from devices heretoforeused for somewhat similar purposes; for instance:

1. It contains no interposed or control electrode of the type ordinarilycalled a grid.

2. Electrons from an incandescent cathode are received by two separateelectrodes.

3. The temperature of the main anode is controlled so as to produce alimited quantity of evaporated molecules of the anode material at ornear its surface.

4. Provision is made to ionize some of these molecules by electronbombardment at a definite rate.

5. In the operation of the device these ions are in part neutralized andin part re-charfred negatively or reionized positively by the lilamentspace charge.4

6. The ionization actions are localized, stable and under completecontrol.

7. Under operating conditions when the anode circuit is opened thecollector current decreases.

I thus produce a vacuum tube detector which shows extraordinary delicacyor sensitiveness to the stimuli of received radio impulses, but which,in contrast to` prior art tubes depending upon random or 11n-localizedionization (which erratic phenomena I prevent by means later to beexplained) is at all times quantitatively governed by the adjustments ofthe circuits.

The scnsitiveness of my new detector may be as great as or greater thanthat of a prior art detector tube used in a regenerative circuit. vet inmy device there occurs no useful radio frequency amplification. Noprovision is lmade to feed back radio frequency currents from indicatorto input circuits and the defects of such a process are avoided. Indeed,the possibility of the tlow ofradio frequency currents in the main anodecircuit may be eliminated by the insert-ion therein of choke coilswithout reducing the responsiveness of the system to received signals.

The construction and operation of my invention may be more clearlyunderstood by reference to the drawings showing one form ofdevice. InFig. 1 an evacuated glass envelope 5 provided with a. stem 6 and press 7contains the three electrodes above referred to. The cathode 8 may be ofthe filamentary 'form (either linear or spiral), for instance oftantalum, tungsten or any of the materials ycommonly used forincandescent filaments,

and is supported by members 9, 10 which are sealed into the press 7 andelectrically connected to the terminals 11, 12. `Terminal 12 is carrieddown the side of the tube and at joint 31 conductively fastened to alength of trical connections with the anode 16.

The vessel is preferably exhausted 'to a high degree by vmodern pumpingmeans, the gases occluded within or upon the internal glass and metalportions of the tube being driven ofl by heating, and the sodium beingintroduced by melting it from a side tube after the tube 5 has beenthoroughly cleaned and evacuated.

F ig. 2 shows the inverted trough collector 15, part of lits support 13,a section of the filament 8, the anode 16, terminal 17, the glasscontainer 5, the heater S2 and its enclosing cement` 84, the view beingtaken at 90 in a horizontal plane fromthat of Fig. 1 to show therelative arrangement of the three electrodes. i

Fig. 3 shows the arrangement ofthe heater 32 and the connectionsthereto, the view being a horizontal cross section of the lovver end ofthe tube.

I have made and successfully used tubes such as those shown in Figs. 1,2 and, in which the cathode consisted of about 1% inch of' 0.004 inchtantaluin Wire. The collector was oit nickel bent from a sheet about 1/2inch square with the formed sides approximately parallel.

The anode was a layer of pure metallic sodium about Z inch in diameterand if., inch thick. andthe distance from the ano-de surface to thecathode Was about 1/4 inch. The peak ot the collector Was about 35 inch`troni the cathode. The heat-er was formed from about 4 inches of' #24resistance Wire, having a resistance of approximately 0.64 ohms.

Fig. 4 shoivs a circuit which I have found satisfactory ttor operationof my tube so as to take advantage of its increased sensitiveness. Inthis diagram the antenna 18 is connected through timing condenser 19 andprimary coil 20 to earth 21. Variably coupled to the primary 20 is asecondary coil 22 having its terminals shunted by a tuning con` denser22'; so as to form an adjustable resonant circuit. From one armature ofthis condenser I provide a direct connection to the ,collector 15 of theintensifying detector tube 5; the other armature ofthe condenser 23 isconnected to the negative terminal of the filament 8, as at the point24, by Way of a potentiometer 25 which is connected in series withresistance unit 36, the two being shunted directly across the filamentbattery 27 as shown. By adjustingr the movable contact of thepotentiometer 25 the collector potential with respect to the negativeterminal of the filament may be varied slightly in either the positiveor negative direction, so as to con- .trol the amount of current flowingthrough the collector filament circuit 8, 32, 24, 25,l 22, 15. The bestpotential for the collector with respect to the negative end of thefilament varies with different tubes, but for the type which I havedescribed may be approximately one volt negative. The current in thecollector-,circuit flows against this potential, which is consequently aneutralizing potential tending to reduce the current Which would flow ifthe collector were connected directly to the negative terminal ofthefilament. Under some conditions it is advisable to make the collectorslightly positive With respect to the` negative end of the-filament, andin this case the current (always flowing from filament to collectorthrough thecircuit) will be in the same direction as the appliedpotential. Nhenth'e collector is made negative with respect to thenegative end of the filament by/ means of potentiometer 25, the appliedpotential is never suflicient to stop completel or to reverse the fiovvof current through t e circuit froin filament to collector, andconsequently the collector never becomes a cathode.

Current for heating the filametary cathode 8 is supplied from thecathode bat-- tery 27 and controlled by the serially connected variableresistance 28. The filament circuit is completed through the heatingresistance 32 and the fixed resistor 35.

. The main anode circuit runs from the common negative point 24 throughthe anode battery 29, which may have a variable potential, and thetelephones to the anode 16.

Obviously the telephones may have substi-I tuted for them any othersuitable translating or coupling device, e. g., a relay, a loud speaker,or the primary ot a transformer leading into an audio frequencyamplifying system. f

.For

In setting up the circuit of Fig. 4 I use coils and condensers of sizesappropriate to the antenna dimensions and the Wave frequencies to bereceived, so. as to bring the resonant adjustments of the tivo radiofrequency circuits Well Within the ranges of the timing condensers 19and 23. For battery 27 I prefer to use three storage cells With a totalvoltage of about 6, since the iilanientary cathode may require from 1.2to 1.4 amperes of current to raise it to the requisite temperature forsufiicient electron emissionf The rheostat 28 may conveniently have aresistance of 8 ohms and the fixed resistor 35 of 0.67 ohms, the heaterbeing of 0.64 ohms resistance as described. The collector potentiometer25 may be of about 100 ohms resistance and the fixed resistor in serieswith it of about 7 5 ohms; the collector current under best operatingconditions is approximately 550 microamperes With most of the tubesWhich I have used. I find that the anode battery 29 may convenientlyhave an clectromotive force of from 10 to 30 volts; since the anodecurrent is ordinarily of about 200 micro-amperes; dry cells are entirelysatisfactory for this circuit. The telephones shown at 30 are ordinarilyof aboutQOO() ohms total resistance to direct current.

To operate my receiver I establish the circuit as shown in Fig. 4, heatthe filament to normal brilliancy and (while listening intheteli-xphoncs) time the primary and secondary circuits to approximateresonance with the frequency of the waves I desire to receive. Havingthus obtained signals, I proceed to intensify these by adjusting thecollector potential and the filament current to their optimum absoluteand i'elative values, as judged by increased strength of the receivedsignals. Occasionally it is found desirable to readjust the radiofrequency circuits to a small extent during this process, but I make noattempt to secure or magnify radio frequency currents in the anodecircuit by tuning, the provision of by-pass condensers or otherwise.

A novel and characteristic feature of the intensification phenomena ofthev preferred form of my device is that when the tube is properlyadjusted the act of opening the anode circuit results in a substantialreduc-y tion in the current flowing in the collector circuit. Forinstance, in one tube the adjustment which gave best response requiredthe collector potential to be 1.4 volts negative with respect to thenegative end of the filament. At this potential the collector circuitcurrent was 600 microamperes flowing in the circuit from the filamentterminal to the. collector (i. e. against this 1.4 volts potential).When the anode circuit was opened the collector current fell to 250microamperes. It is apparent therefore that the collector circuit inthis new device performs a very different function from the usual gridor control circuit.

In receiving radio telephone signals on my intensifying detector one isstruck by their loudness and clarity and, in contrast to'their receptionon regenerative devices, the absence of distortion which would becausedeither .by internal beating, self-oscillations or too order to securemany df its benefits. Many modifications of structure and connectionsywill at once occur to those skilled in the art; for instance, the deviceof Fig. 1 may be utilized quite effectively in capacity-coupled or inaudio transformer radio circuits such as are' common in radio reception.

One need not even use exactly the form of tube shown in Fig. 1; forinstance, the anode material may be contained in an insulating orconducting cup instead of lying directly upon the glass wall of thetube. I have also secured goed effects from specially constructedoutside anode tubes embodying some of the principles set forth in myUnited States- Patent #1,291,441, though it is desirable to modify theinternal electrodes as described herein. The intensification effectssecured by the presentinvention are greatly reduced or even prevented ifthe collector electrode pro- ]ects between the cathode and the mainanode,

i as would be the caseA if it were attempted to use an interposed gridas the collector. When.`

using an external anode tube the sodium or otheil ionized material,which'is apparently necessary to co-operate in the newly diseov? eredphenomenon of intensification, may be providedby electrolysis of theglass wall convenient and preferred but not essential for I have securedgood results by using two electrically connected plates, one on eitherside of the cathode and parallel thereto, placed edgewise with respectto the main anode.

I have found that the temperature of the anode during operation shouldbe kept within limits which depend upon the material used, though withinthese limits it is not especially critical. If the anode temperature israised labove a certain value, for any particular anode material used,there is likely to be so great an increase in vapor density within thetube, at points remote from the anode, as to set up random orun-localized ionization which may materially reduce the scnsitiveness ofthe system. When sodium is used for the anode of such a tube as I havedescribed, the temperature of the anode becomes suf'- ciently high toprovide requisite particles for ionization within a few seconds afterthe filament circuit is closed. Heat from the filament is radiated tothe anode surface and even at the relatively lonr temperature thusproduced there is a considerable emission of particles from the anode.As time goes on,

however, this original emission will decrease,

i, and might become only a small fraction of its initial value. Soonafter the filament is turned on, however, heat from the external heater32 will reach the anode through the 12o glass tube, and, by properlychoosing the size of this heater and the current therethrough, thetemperature of the anode may be increased at a rate which will verynearly compensate for the decrease in original emission above described.Thus particles lfor ionization may be provided for an indefinitely longtime at an approximately uniform rate. The effect of the heater 32 maybe sufficient to liquefy certain anode materials, such as sodiuni, andconsequently it is desirable to op- -erate the tube in the positionshown in Figs. 1 and 2 so as to retain the anode material in positioneven though molten.

Sodium is a particularly desirable metal` for tubes utilizing thissignal intensifying effect, but I do not desiie to be limited to mainanodes formed of this metal, since I have secured excellent operationfrom tubes having anodes of other metals, including potassium, and fromalloys such as sodium and potassium in equal proportions, alsotellurium, lithium and mercury. Itdoes not appear essential to utilizehighly electropositive `metals althrough those cited are convenient. Thebest condition for control of ionization at the anode surface appears tobe most easily maintained with the anode heated slightly above itsmelting point, and hence it is desirable to use anodematerials whichmelt at relatively low and easily attainable temperatures. From myexperience with these intensifying tubes it appears that there shouldbepresent a controlled quantity of molecules or atoms vapor-izedpreferably from the anode, that the greatest density of these moleculesor atoms should preferably be limited to the immediate neighborhood ofthe anode siii'- face, and that by bombardment of these lovcalizcdmolecules or atoms there shouldA be produced a controlled amount ofpositive ionization within a zone near the anode surface. Random orunlocalized ionization throughout the tube should be prevented,preferably by complete exhaustion of included gases so as to obviate thepossibility of gas ionization in the space and by maintaining the vapordensity of the anode material comparatively low within the body of thetube. I prefer to opei'ate the tubes at the lowest feasible temperatureconsistent with sufficient localized ionization, so as to reduce thevapor pressure of the anode material to such a degree that the chance offorming ions by electron collision with vapor molecules in the evacuatedspace away from the electrodes is minimized.

Although I have shown the telephone'or other indicating instrumentassociated directly with the main anode circuit, I do not wish to belimited to such connection. The

constantly flowing currents in both the anode and the collector circuitsare normally reduced upon the arrival of signals, the amount of suchreduction being substantially in beth circuits and reproducing thesignal variations or modulation. It is more convenient to-use thetelephones, oi transformer for audio frequency coupling, in the niainanode circuit since the impedance of the anode cicruit is considerablyhigher than that of the collector circuit and hence is better suited tothe accessories available on the market.

The phenomena which underlie the operation of my new device are quiteobscure and complicated, although its desirable effects are easilyobtained and controlled in the manner I have described. Vithout desiringto be limited by any statement of theory, I- may say that thearrangement acts as though the collector circuit current pulsatescontinuously with small amplitude at a frequency which depends upon thetube constants vand adjustments but is necessarily much lower than thefrequency of the signals to which the greatest response is given. Thispulsation appears to' trons from the space charge, thus becoming`recharged negatively, that others stiikc electrons with sufficientvelocity to become reionized positively, and that many of the particlesionized at the anode/and accelerated toward the cathode finally strikeeither the cathode or the collector. It also appears that for a time,the percentage of positives and negatives reaching the collector is suchthat more and more ionization takes place, thus building up thecollector current until at some final value the current falls to a lowervalue. The time of this pulsation may be something like 1/100000 second,and (under operating adjustments) the cycle is continuously repeated.

Vhen radio signals of a substantially liiglici l frequency are appliedto the collector circuit, the ionization appears to be broken up to anextent dependent upon the intensity of the applied signal, so that thereoccurs a substantial fall of average collector current, which fall isproportional to the signal strength. rlhereafter a certain time isrequired to reach the state of equilibrium at the higher slightlypulsating value of collector current. It has been found that for apulsation frequency of 70000 cycles per second, no substantial responseis had for applied signals of frequency lower than about 800000 cyclesbut a rapidly increasing sensitiveness `is found as the signal frequencyis increased above this value to 75000() cycles or more. By changing theproportions and adjustments of the system it is feasible to change thesensitive frequency range. rlhe average current in the anode circuitfollows the audio frequency variations in collector current, and hencetelephones connected in either circuit respond to the signalfluctuations.

An effect which is of value in the operation of this tube is theincrease of electronic cinissien from the cathode at any giventemperature caused by the presence of sodium or the like. In my Patents1,477,868 and 1,477,869 I have disclosed means for increasing elec- Inthe present new form of tube, sodium for this purpose may be derivedfrom the anode. As may easily be understood, some of the positive sodiumions produced at or near the anode y are attracted to the filament anddeposited p thereon, losing their charge and becoming simply sodiummolecules. I have found that a cathodewhen so coated with sodium emitselectrons at a given rate when maintained at a substantially lowertemperature than would a simple ilament of tungsten, molybdenum ortantalum. Unless the sodium coating is continually renewed by arrival ofions from the anode or otherwise it will in time pass oli' into thespace as a neutral vapor and become exhausted, but in the structure Ihave shown there is provision for such continuous renewal. To securethis effect to the most useful degree it is desirable that the sodiumshould reach' the filament in ionic form, and consequently the operationof a simple cathode in an atmosphere of neutral sodium vapor isordinarily insufficient and the full e`ect will not be had unless thesodium is at least in part ionized. Similar effects are had from otherelectropositive metals which I have described as useful in this type oftube, although the increase of emission for a given temperature ispartly incidental to and independent ot the sensitive detection efectsdescribed.

For convenience, in mounting I prefer to carry the four terminals 1l,33, 14 and 17a to the contacts ot' a standard four-prong lamp base suchas is commonly used with three electrede vacuum tubes. lo preventspilling when a molten anode is used, the tube may be operated in theposition shown by Figs. 1 and 2 or the lamp base mav be mounted belowthe main anode (which is in this instance carried by a depression in orcup attached to the top of the stem), the lilament and collectorsupporting wires running downward through the press and stem, but theanode, cathode and collector being maintained in substantially the samerelative positions shown in the drawings. Other Variations of structureand adaptations of the principles and 'novel'fea' minal cathode, ananode,

tures of the invention herein disclosed Will occur to those familiarwith the use of vacuum tubes in high frequency. signaling.

I claim:

1. A vacuum tube containing an alkali metal anode, a curved electrode, adouble terminal cathode interposed between said anode and said electrodeand disposed substantially at the center of curvature of said curvedelectrede, and a resistance element in series with said cathode andcontiguous to said tube.

2. A vacuum tube having a press and containing an alkali metal anode, acurved elec- Itrede, a double terminal cathode-interposed between saidanode and Said electrode, leadin wires for said electrodes, all of saidlead-in wires passing through said press, and a resistance element inseries with said cathode and contiguous to said tube.

3. An electric discharge device comprising a base, an envelope disposedon said base and containing an alkali vapor, a double tera controlelectrode, and means in the base to heat said anode. n

4. An electric discharge device comprising a base, an envelope disposedon said base and containing a vapor, a cathode, control and anodeelectrodes, and means in said base to heat one of said electrodes.

5. An electric discharge device comprising a base, an envelope disposedon said base and containing an alkali vapor, a cathode electrode, acontrol electrode, and an anode electrode composed of an alkali metal,and means in said base to heat said anode electrode.

(i. An electric discharge device comprising an envelope containing analkali vapor, `a cathode, a control and an anode electrode, said cathodedisposed between said control and anode electrodes, and electricalmeans, exterior of said envelope toheat said alkali vapor while saiddevice is in operation.

7. An electric discharge device comprising an envelope containing avapor, a double terminal cathode, a control and an anode electrede, andan electrical resistance means exterior of said envelope to heat saidvapor, said electrical resistance means and said double terminal cathodebeing connected serially.

HAROLD PoTTERnoNLE.

